Twilight's growth
by GeekC
Summary: Twlight's flight training with Rainbow motivated her to build some muscle. Muscle growth inside. Rated M for nudity and strong innuendos.


******A/N: this is my second Female Muscle Growth story after _Misty's drink_.**

******Disclaimer: I do not own My Little Pony, nor the characters from it. I do not make any money from the writing of this story.**

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**Twilight's growth**

Since she gained her wings, Twilight Sparkle had been taking flight lessons twice a week with Rainbow Dash. Truth be told, regarding flying, Twilight was a slow learner.

According to Rainbow, Twilight's flight problems can be attributed to weak back muscles. That is why the flying sessions were quickly doubled by gym sessions.

There, Rainbow showed her the machine to use for working out her back muscles. As she showed her the appropriate movements, Twilight had a good view of her friend's toned body, closely hugged by her sport bra and shorts.

Working out since she was a filly, Rainbow had a perfect toned body with well defined, but not too bulgy, muscles. Twilight was fascinated by her arm's muscles rippling under her skin as she demonstrated the movement.

While Twilight had her turn on the machine, Rainbow went to another machine.

As they were showering together after some more workouts on other machines, Twilight lost herself in the sight of the water running all over Rainbow's body: her back, her legs, and particularly her abs...

"Rainbow? Can you rub my back? It hurts a little after that workout."

"Sure."

As Rainbow rubbed her back, Twilight let out small satisfied moans. Once Rainbow was done, Twilight turned around, and give her a hug. As she was hugging her, her hand slowly went down Rainbow's back, her fingertips detailing each muscle, to reach her butt. Surprised, Rainbow pushed her away.

"Let me at least touch your abs."

Rainbow let her do as she wanted, and soon after they ended their shower.

That night, as she was slowly falling asleep, Twilight took a decision: the weak bookworm she always had been shall become as fit as Rainbow.

And thus, Twilight doubled her effort at the gym, but little to no progress can be seen. She then asked Rainbow about some workout she could do at home. But even with this, the only results were sore muscles.

Another night, after another gym session and some home workouts, as she was lying in her bed, Twilight decided to look for something about muscle building in her books.

- xxx -

The next day, she spent the morning and much of the afternoon leafing through dozens of medicine or self improvement books, but to no avail. As she put back the last book on the shelves, she made the one beside it fall. It had opened in its fall, so when she picked it up, she immediately checked the pages to look for any deterioration. Seeing not a single dent, she started to read the page the book had fallen on.

It was about a simple formula to ease transit with a metabolism boost. Twilight got an idea: why not use the metabolism boost this formula procured to boost her muscle building?

So the next training day, just before leaving the gym's changing room, she cast the formula on her. As its effects last for many hours, it would still be effective in the evening when she would do her home workouts. At the end of the day it felt as if she had worked out thrice as more as she really did, and she had no difficulties falling asleep.

The next morning, as she was under her shower, she was surprised to feel her body slightly firmer than the previous day. To be sure, she decided to use the formula again, but it would have to wait the next training session, as she had other things planned for the following days.

- xxx -

Back to the gym, like the previous session, she cast the formula on her just before leaving the changing room. And as the previous time, at the end of the day, it felt as if she had worked out far more than she really did.

The next morning, she was delighted to feel her definitely firmer body, which even started to slightly show some muscles. She was now determined to put more effort in her magically enhanced training, and to work out more at home.

The following weeks she worked out at the gym twice as she did in the first weeks, and worked out at home, even the days when she did not train with Rainbow. And in one month time, she had acquired a very athletic figure, but still not as fit as Rainbow, and her flying skills had increased.

- xxx -

Even if she was now a really skilled flier, Twilight still continued her training with Rainbow. These trainings were making her feel better, and she really liked the new body she had acquired thanks to her own magically enhanced training.

As Rainbow and Twilight were showering after one of their workout sessions, Rainbow noticed the change in Twilight's figure.

"Whoa Twilight, I've never noticed how fit you've become. Looks like my advices are starting are starting to bear fruit."

"Yeah. And I feel really great now that I'm training like that. Look at that new body!", she said posing.

"You look indeed quite athletic, but not as much as me!", boasted Rainbow also posing.

Approaching Twilight from behind, Rainbow put her hands on Twilight's stomach: "Hmm... Not bad... But I know you can do better than that".

Sliding her hands up along Twilight's stomach, she reached and grabbed her breasts: "Nice pecs...".

Turning back, Twilight grabbed Rainbow in a close hug, and kissed her while rubbing herself up and down against Rainbow. Breaking the kiss, Twilight trailed her tongue down Rainbow's jaw to her neck and then to her breasts.

While taking care of Rainbow's chest, Twilight grabbed her butt, and slowly reached between her legs. Due to Twilight's deftness, it was not long before Rainbow was shaken by a huge orgasm and fell limply in Twilight's arms.

As they were dressing up, Rainbow seemed grateful for what just happened in the showers.

That evening, as she was lying on the floor sweating and panting after her home workouts, Twilight thought again about what happened in the showers. She put her hands where Rainbow had put hers, and slowly start to masturbate. While groping her breasts, the hand on her stomach slowly slipped between her legs. After having climaxed and made some poses naked in front of her mirror, admiring her fit body glistening with sweat, she went to shower.

After a quick shower, she directly went to bed, and read some time lying naked on her side, turning around from time to time.

- xxx -

Thanks to a great dedication the following weeks, it was not long before Twilight reach her initial objective, i.e. being as athletic as Rainbow.

One training day, as they were changing before their gym session, Twilight stood naked in front of an equally naked Rainbow.

"Hey, Rainbow. What do you think of that?", she asked with a smirk.

"My, my Twilight. Look at you! You're as big as me now. It's incredible how quickly you changed from bookworm to muscle goddess."

_Muscle goddess? Eh, wait for what I still have in store. With my training I will outgrow you quickly!_, thought Twilight.

Rainbow approached Twilight, and slid her hands all over her body, groping here and there: "Whoa... Never thought my advices would be that effective... It's amazing...".

During that day's training, it was Rainbow who looked fascinated at Twilight. After the training, as they were walking to the showers, she grabbed Twilight's butt. Under the shower it was Rainbow who hugged lovingly Twilight and kissed her. Breaking the kiss, she trailed her tongue all along Twilight's front: her neck, her chest, her stomach... With her tongue and her fingers she slowly build Twilight's excitation... After her body had stopped shaking from the orgasm, Twilight gave Rainbow a tender thank you kiss.

As they were dressing up, Twilight asked Rainbow: "Do you think we can train naked? I really got used to my naked home training, and I feel restrained by my sport clothes." Rainbow answered: "As long as we are alone in the gym I see no problem. To be honest, I also like to train naked. I really like the sight of my sweaty body." It was then agreed that from now on, they would train naked.

Back at her house, motivated by Rainbow's remark about her having become a 'muscle goddess' to grow even more, decided to cast upon herself another metabolism boosting spell while the previous one was still effective. After having checked for any side-effects to a double cast, she did it. As she trained, she felt the strain she got used to increase a lot, and at the end of her training she felt as if she had lifted a dragon and its jewel trove. Just before showering for the night, she flexed in front of her mirror, and it looked like she was slightly bigger than just after the gym. Under the shower, she also felt her body had hardened.

- xxx -

The day of their first nude workout session, in the changing room, after they had undressed, Rainbow handled Twilight a small bottle.

"What's that?", asked Twilight.

"It's just some oil to make our already beautiful bodies even more sexier when we will be working out."

Then, after having oiled themselves, our two muscle goddesses went into the gym. As they were working out, they observed each other. Twilight was finishing with a machine and still sitting on the bench when Rainbow joined her.

She whispered into Twilight's ear: "To see you working out like that... It turned me so on...".

Twilight answered by a kiss and her hands on Rainbow's oiled chest. Rainbow pushed her down to the machine's bench and spread Twilight's legs to put one between her own.

As she was tongue wrestling with Twilight, she placed her hands on Twilight's chest. While one hand remained on Twilight's chest, the other was slowly crawling to her crotch. When she started her ministrations between Twilight's legs, she began rubbing her crotch on Twilight's leg, in sync with her fingers. Soon they were both shaken by a big orgasm, and Rainbow slumped limply on Twilight.

As they were catching their breath, they slid their hands in the other's mane and exchanged little swift kisses. Then the two oiled amazons went showering, and parted in front of the gym after a last kiss.

What happened that day motivated Twilight to become even more ripped than Rainbow. In order to do that, she would always work out with a double cast of her enhancing spell.

- xxx -

After one week of intense home workout under a double cast of her spell, Twilight had acquired huge bulging muscles, bigger than Rainbow's.

The day of their gym session, Rainbow did not left her time enough to undress: as soon as they entered the changing room, Rainbow jumped on her and proceeded to tear away her clothes to gain access to her muscular body. Once she had completely undressed Twilight, she made a short strip-tease, and then they make out on the floor, with her taking the lead.

While kissing her, she rubbed her hands all over her body: her muscular chest, her abs... Breaking the kiss she went directly for Twilight's core. Using her tongue and her fingers, she slowly lead Twilight to her climax. Once they both had catch their breath, they oiled each other and went to the gym.

As they were working out, Rainbow asked Twilight: "Say Twilight, how did you do to gain so much muscle that quickly?".

"To be honest Rainbow, I used some magic to boost my muscle building. The first time we went here, viewing your muscle while you show the moves to use with each machine motivated me to build some muscle. But as my efforts were not rewarded in the first place I looked for some spell to help me. At first I used a single cast, and then a double."

"Can I have a try next time?"

"Sure!"

As usual after their workout they showered, and parted in front of the gym.

- xxx -

The next workout session, Rainbow directly asked Twilight for a double cast of her spell.

Likely due to Rainbow already athletic condition, the spell had a surprising effect on her: as she was working out, Twilight could see Rainbow grow with each flex or pump, right under her eyes... And at the end of the session, Rainbow had grew as large as Twilight.

Viewing Rainbow grow under her eyes had turned Twilight so on that as soon as they entered the showers she pined Rainbow on the wall with a kiss, while her hands ran all over Rainbow's body. Breaking the kiss, she licked Rainbow's nipples and placed a hand between Rainbow's legs and hers. Her fingers went in synch with her licks. Her own arousal was such that she came first, and it was her hand contracting between Rainbow's legs that finished her.

As they sat limply on the floor catching their breath, Twilight asked Rainbow how she had felt when she grew. After Rainbow had given her impressions, Twilight also wanted to experience this. They then convened that their next training session would be done under a triple cast of the boosting spell for both.

- xxx -

Twilight was so impatient for their next training that time seemed to pass two times slower, and when the day came, she was as excited as a filly in front of his Christmas presents until the scheduled time.

Rainbow was waiting for her in front of the gym, and when she saw her, she skipped toward Twilight to greet her. It was quite funny to see a beautiful muscular pony acting like a filly.

The two of them were so impatient that they did not wait to be in the changing room to undress.

"Come on, come on Twilight! Quick, quick, quick!"

After three cast of the spell, Twilight felt a strange tingling sensation, and Rainbow looked like she did too. Then our two muscle goddesses started working out.

With each flex, Twilight felt the tingle increase, and saw her muscles slowly swelling. In the mean time she felt an arousal slowly building up, with some stronger increases each time she looked at Rainbow. Rainbow seemed to feel the same, as they often exchanged slutty stares.

After a while, Twilight's arousal was so high that she felt like she would burst if she did nothing, and Rainbow looked like she was feeling the same.

And in a blink, they rushed into each other's arms and started a tender and passionate wrestling. For an hour they wrestled: tongue against tongue, muscular arms and legs locked together, sweaty body against sweaty body... Then they lay limply on the floor catching their breath, with a bright smile on their face.

Going to the shower room, they noticed they grew so much that they had some difficulties walking through the door. As they let the water flowing down their huge muscular bodies, they decided that from now on, their training sessions would be for maintenance.

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**A/N: I hope you liked reading this story as much as I enjoyed writing it.**


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